What does a multiplier of 0.75 mean, and how is it represented mathematically?

A multiplier of 0.75 means that any value it is applied to will be multiplied by 0.75. This is equivalent to taking $75\%$ of the original value, or reducing the original value by $25\%$.

For example, if an original value is $X$, the new value after applying the multiplier will be:

$$\text{New Value} = X \times 0.75$$